[KEP-5004] DRA Extended resource documentation

Author: yliaog

content/en/docs/concepts/scheduling-eviction/dynamic-resource-allocation.md

@@ -424,6 +424,39 @@ create ResourceClaim or ResourceClaimTemplate objects in namespaces labeled with
 `adminAccess` field. This ensures that non-admin users cannot misuse the
 feature.
 
+### Extended resource {#extended-resource}
+
+{{< feature-state feature_gate_name="DRAExtendedResource" >}}
+
+You can provide an extended resource name for a DeviceClass. The scheduler will then
+select the devices matching the class for the extended resource requests. This allows
+users to continue using extended resource requests in a pod to request either
+extended resources provided by device plugin, or DRA devices. The same extended
+resource can be provided either by device plugin, or DRA on one single cluster node.
+The same extended resource can be provided by device plugin on some nodes, and
+DRA on other nodes in the same cluster.
+
+In the example below, the DeviceClass is given an extendedResourceName `example.com/gpu`.
+If a pod requested for the extended resource `example.com/gpu: 2`, it can be scheduled to
+a node with two or more devices matching the DeviceClass.
+
+```yaml
+apiVersion: resource.k8s.io/v1beta2
+kind: DeviceClass
+metadata:
+  name: gpu.example.com
+spec:
+  selectors:
+  - cel:
+      expression: device.driver == 'gpu.example.com' && device.attributes['gpu.example.com'].type
+        == 'gpu'
+  extendedResourceName: example.com/gpu
+```
+
+Extended resource is an *alpha feature* and only enabled when the
+`DRAExtendedResource` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/)
+is enabled in the kube-apiserver, kube-scheduler, and kubelet.
+
 ### Prioritized list {#prioritized-list}
 
 {{< feature-state feature_gate_name="DRAPrioritizedList" >}}

content/en/docs/reference/command-line-tools-reference/feature-gates/DRAExtendedResource.md

@@ -0,0 +1,16 @@
+---
+title: DRAExtendedResource
+content_type: feature_gate
+_build:
+  list: never
+  render: false
+
+stages:
+  - stage: alpha
+    defaultValue: false
+    fromVersion: "1.34"
+---
+Enables support for the [Extended Resource](/docs/concepts/scheduling-eviction/dynamic-resource-allocation/#extended-resource)
+feature. It makes it possible to specify an extended resource name in a DeviceClass.
+
+This feature gate has no effect unless you also enable the `DynamicResourceAllocation` feature gate.